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Routing table

Posted on 2006-05-18
Medium Priority
Last Modified: 2010-03-19
Hi All,

I am a new learner to configure a router. The rotuer I am using is 3Com NetbuilderII.

I have configured the 3 network interface cards as follows:

Port 1:
Port 2:
Port 3:

I have also disabled RIP & OSPF service.
Port 3 will be connected to a firewall with IP address
Any problem with my configuration like this?

Further, I would like to know whether the rotuer can learn routes by itself or do I need to enable any service/traffic?


Question by:ee_lcpaa
  • 2
  • 2

Author Comment

ID: 16714816
Sorry, supplementary information.

My firewall has 2 ports with IP address & (same subnet as port 3)

I also have a question like this. If I have another PC with IP connected directly to the FW port with IP Then I start a ping service to

Under my configuration, will the ping succeed?
I wonder the router will learn a route that src IP will route through port 3( Am I right? Please advise. Thanks a lot.

Please note the FW will not discard the ping service.
LVL 20

Expert Comment

ID: 16715080
 Disclaimer: I'm not familiar with 3Com Netbuilder, but standard routing principles & IP behavior still apply here.

>If I have another PC with IP connected directly to the FW port with IP Then I start a ping service to ...will the ping succeed?
  It should succeed IF: A) is assigned to one of the router's interfaces, B) the default gateway for the PC is,  C) there aren't any rules blocking ping traffic between the hosts,  D) no software firewall on the is blocking ping traffic, & E) you've got a crossover cable between the PC & the router interface (if it's a typical router interface).

>...would like to know whether the rotuer can learn routes by itself or do I need to enable any service/traffic?
  A router can't learn routes automatically if all dynamic routing protocols (ie, RIP or OSPF "services") are disabled.  If RIP & OSPF are disabled, the only way it's going to learn a new route is if you manually configure a static route.

>Port 3:
>My firewall has 2 ports with IP address & (same subnet as port 3)
  I hope the router didn't allow you to set another port to w/ the same subnet mask as port 3?!  If so, then I'd expect your router to be confused when trying to route traffic to/from IPs in this subnet, since overlaps the range of valid IPs for the subnet on port 3.


Author Comment

ID: 16715515
Dear calvinetter,

You said the ping service will be succeeded. I would like to give you a clear picture. The configuration is as follows:

PC (> ( F/W with 2 ports ( --> Router (Port 3, one of the ports with this IP)

Please note the testing PC will not be connected directly to the router. There is a FW between them. Under this configure, Will the ping service be suceeded from PC ( to (port 1 of router)?

From you second point, after disabling the RIP & OSPF service, the router will not learn anything. I have a question that how can the router know that the returning path to is through Port 3 --

Please advise.
Thanks a lot.
LVL 20

Accepted Solution

calvinetter earned 600 total points
ID: 16721221
Ok, thanks for the clarification & the diagram.  To answer both your questions in your latest post - Based on your latest post above, you should be able to ping port 1 of the router IF the default gateway for the firewall is the port it's connected to (, & IF either of the following conditions are met:  
either A) the FW is NAT'ing the 10.11.2.x subnet to the 10.12.4.x subnet,
or B) you configure a static route on the 3Com, to point a route for the 10.11.2.x network to the FW's IP of
  (And of course, as long as the firewall or the router isn't blocking ping traffic through it.)


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